European Union President Donald Tusk traveled to Balkan capitals on March 2 to discuss recent restrictions they imposed on migrants at their borders.

He is visiting the Croatian capital of Zagreb and the Macedonian capital of Skopje, where leaders recently announced they are considering even more drastic measures to shut down the so-called Balkan route traveled by migrants to get from the Middle East to northern Europe.

His trip comes as the United Nations refugee agency warned that the EU is on the "cusp of a self-induced" humanitarian crisis if governments fail to work together.

The border restrictions imposed by Macedonia and other Balkan countries as well as Austria have contravened advice and policies advanced by the EU.

They have also had the effect of creating a "domino-like" buildup of tens of thousands of refugees left stranded in Greece.

After visiting the Balkans, Tusk on March 3 and 4 will travel to Turkey, where most of the refugees from Iraq and Syria pass through on their way to Europe.